JP7141189B2 - Pigment-containing resin composition - Google Patents

Description

The present invention relates to a pigment-containing resin composition, a method for producing the same, an inkjet recording ink containing the pigment-containing resin composition, and a method for producing the ink.

Inkjet printing is printing in which ink droplets are directly ejected from extremely fine nozzles onto a printing medium and adhered to record characters and images. This method has the advantages of low power consumption and non-contact with the print medium, and has become very popular in recent years. Among them, the drop-on-demand system, in which ink droplets are ejected only when recording is required, has become mainstream.

Furthermore, in recent years, pigments have been widely used as colorants in order to impart weather resistance and water resistance to printed matter. When a pigment is used, the ink may be prepared by mixing an aqueous pigment dispersion in which the pigment is finely dispersed in an aqueous medium (hereinafter also referred to as an "aqueous pigment dispersion") and a water-soluble organic solvent as a moisturizing agent. . However, in curable inks that are cured by ultraviolet light and are used for printing on non-water-absorbing printing media such as resin films, water is not used because the main component of the ink is an organic compound having a polymerizable functional group. and the pigment cannot be prepared and blended as an aqueous pigment dispersion.
On the other hand, in water-based inks, which are used as inks with low environmental load, water-based pigment dispersions are used in the preparation of inks. Alteration due to the generation of microorganisms becomes a problem.
In order to overcome these problems, attempts have been made to use fine pigment particles obtained by finely dispersing a pigment in a medium such as water and then removing the medium.

For example, Patent Document 1 describes a photocurable liquid ink containing a colorant and a curable liquid that is cured by light, and describes that colored resin particles used in the ink are obtained by freeze-drying. there is
Patent Document 2 discloses a pigment composition obtained by dispersing an aqueous wet cake of a pigment and an aqueous resin in an aqueous solvent, and then separating and removing the aqueous solvent, wherein the aqueous resin has a specific glass transition temperature. and a resin partially or wholly soluble in an aqueous solvent, wherein the aqueous solvent is water, one or more water-miscible organic solvents, or mixtures thereof. .
US Pat. No. 6,200,401 discloses a solid pigment preparation containing a pigment and a dispersant resin for the purpose of providing a stable, well-dispersed pigment-containing paint, wherein the dispersant resin is a pendant wherein the dispersant resin contains a specified amount of alkylene oxide units and has a number average molecular weight within a specified range It is

JP 2011-178948 A JP 2009-120658 A Japanese Patent Publication No. 2009-510245

However, it has been found that with the techniques of Patent Documents 1 to 3, it is difficult to ensure the dispersion stability of the pigment in the dispersion obtained by blending the pigment fine particles and in the ink. When a styrene-acrylic resin is used as a pigment dispersing resin, the pigment dispersing stability may not be sufficient. In addition, when a polyester resin is used as a pigment dispersing resin, although the dispersion stability of the pigment is improved, the particle size is too large to be used as the pigment fine particles of the ink for inkjet recording. was virtually impossible.
Since the dispersion stability of pigments affects the color tone during printing, there is a demand for further improvement in the dispersion stability of pigments.
The present invention provides a pigment-containing resin composition that has no risk of deterioration due to the generation of microorganisms, has excellent pigment dispersion stability, and can be used for both aqueous inks and non-aqueous inks, and a method for producing the same. An object of the present invention is to provide an inkjet recording ink containing the pigment-containing resin composition and a method for producing the ink.

The present inventors have found that at least one anionic group of a resin having an anionic group and a polyester structure is used as a dispersing resin having a function of stably dispersing a pigment when used in a dispersion or an ink. The above problem is solved by setting the average particle size of the water dispersion in which the obtained pigment-containing resin composition is dispersed at a predetermined concentration in a specific range using a resin obtained by partially neutralizing the resin with a neutralizing agent. I found what I could do.

That is, the present invention provides the following [1] to [4].
[1] A pigment-containing resin composition containing a pigment and a resin (A), wherein the pigment-containing resin composition satisfies the following conditions 1 to 3.
Condition 1: The resin (A) has an anionic group, and at least part of the anionic group of the resin (A') containing a polyester structure is neutralized with the neutralizing agent (b).
Condition 2: The content of volatile substances in the pigment-containing resin composition is 1% by mass or less.
Condition 3: A water dispersion (α) obtained by dispersing the pigment-containing resin composition in water so that the concentration of the pigment-containing resin composition is 2 × 10 ^-4 % by mass, measured by dynamic light scattering method. The average particle diameter obtained by cumulant method analysis is 0.5 μm or less.
[2] An inkjet recording ink containing the pigment-containing resin composition described in [1] above.
[3] A method for producing a pigment-containing resin composition according to [1] above, including the following Step I and Step II.
Step I: A step of mixing and dispersing water, a pigment, a resin (A′), and a neutralizer (b) to obtain an aqueous pigment dispersion (D) Step II: The aqueous pigment dispersion obtained in Step I A step of drying (D) to obtain a pigment-containing resin composition having a volatile substance content of 1% by mass or less, wherein the aqueous pigment dispersion (D) contains a pigment and a resin (A). and an average particle size of 0.5 μm or less as determined by a cumulant method analysis measured by a dynamic light scattering method.
[4] The method for producing an inkjet recording ink according to [2] above, which includes the following steps I to III.
Step I: a step of mixing and dispersing water, a pigment, a resin (A′), and a neutralizing agent (b) to obtain an aqueous pigment dispersion (D);
Step II: A step of drying the aqueous pigment dispersion (D) obtained in Step I to obtain a pigment-containing resin composition having a volatile substance content of 1% by mass or less Step III: The pigment obtained in Step II A step of mixing the contained resin composition and a liquid compound to obtain an inkjet recording ink Here, the water-based pigment dispersion (D) contains the pigment and the resin (A), and is dispersed by a dynamic light scattering method. The average particle diameter determined by the measured cumulant method analysis is 0.5 μm or less.

INDUSTRIAL APPLICABILITY According to the present invention, a pigment-containing resin composition that is free from deterioration due to the generation of microorganisms, has excellent pigment dispersion stability, and can be used for both aqueous and non-aqueous inks, a method for producing the same, and the An inkjet recording ink containing a pigment-containing resin composition and a method for producing the ink can be provided.

[Pigment-Containing Resin Composition]
The pigment-containing resin composition of the present invention (hereinafter also referred to as "pigment-containing resin composition") is a pigment-containing resin composition containing a pigment and a resin (A), and satisfies the following conditions 1 to 3. .
Condition 1: The resin (A) has an anionic group, and at least part of the anionic group of the resin (A') containing a polyester structure is neutralized with the neutralizing agent (b).
Condition 2: The content of volatile substances in the pigment-containing resin composition is 1% by mass or less.
Condition 3: A water dispersion (α) obtained by dispersing the pigment-containing resin composition in water so that the concentration of the pigment-containing resin composition is 2 × 10 ^-4 % by mass, measured by dynamic light scattering method. The average particle diameter obtained by cumulant method analysis is 0.5 μm or less.
In the present invention, the term "volatile substance" means a substance that volatilizes at normal temperature and normal pressure, specifically a substance that has a vapor pressure or sublimation pressure of greater than 1 kPa at 25°C and contains water.

The pigment-containing resin composition of the present invention has no risk of deterioration due to the generation of microorganisms, and the dispersion stability of the pigment in the dispersion obtained using the pigment-containing resin composition or the ink containing the pigment-containing resin composition (hereinafter also referred to as “pigment dispersion stability”), and can be used for both aqueous and non-aqueous inks. The reason is presumed as follows.
First, when the content of volatile substances in the pigment-containing resin composition satisfies the numerical range of Condition 2, the generation of microorganisms due to inclusion of water is suppressed, and deterioration can be prevented. In addition, when the resin contained in the pigment-containing resin composition satisfies the above condition 1, the dispersion stability of the pigment is improved due to the electrostatic repulsion due to the anionic group of the resin and the affinity of the polyester structure for the pigment particles. Conceivable. Furthermore, by satisfying the numerical range of Condition 3 above, the dispersion stability of the pigment is improved, and coarse particles are reduced. can be reduced. Therefore, it is considered that the storage stability and ejection properties are improved when used in ink.

<Pigment>
Pigments used in the present invention may be either inorganic pigments or organic pigments, and lake pigments and fluorescent pigments may also be used. In addition, if necessary, they can be used in combination with an extender pigment.
Specific examples of inorganic pigments include metal oxides such as carbon black, titanium oxide, iron oxide, red iron oxide and chromium oxide, and pearl luster pigments. Carbon black is preferable as the pigment used in the black ink. Examples of carbon black include furnace black, thermal lamp black, acetylene black, channel black and the like.
Specific examples of organic pigments include azo pigments such as azo lake pigments, insoluble monoazo pigments, insoluble disazo pigments, and chelate azo pigments; Examples include polycyclic pigments such as linone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, and threne pigments.
The hue is not particularly limited, and achromatic pigments such as white, black and gray; and chromatic pigments such as yellow, magenta, cyan, blue, red, orange and green can be used.
Specific examples of preferred organic pigments include C.I. I. Pigment Yellow, C.I. I. Pigment Red, C.I. I. pigment orange, C.I. I. pigment violet, C.I. I. pigment blue, and C.I. I. One or more types of each product number selected from Pigment Green.
Examples of extender pigments include silica, calcium carbonate, and talc.
A pigment can be used individually by 1 type or in mixture of 2 or more types.

(Condition 1)
<Resin (A)>
In the pigment-containing resin composition of the present invention, the resin (A) has an anionic group, and at least part of the anionic group of the resin (A') containing a polyester structure is replaced with the neutralizing agent (b). It satisfies the neutralization (condition 1).
The resin (A) has a function as a pigment dispersant that exhibits a pigment dispersing action when the pigment-containing resin composition is used in an aqueous pigment dispersion or an ink, and a function as a fixing agent for printing media.
The anionic groups in the resin (A') are dissociated to release hydrogen ions, such as carboxy groups (--COOM), sulfonic acid groups (--SO ₃ M), and phosphate groups (--OPO ₃ M ₂ ). Groups exhibiting anionic properties by means of such groups, or their dissociated ionic forms (-COO ^- , -SO ₃ ^- , -OPO ₃ ^2- , -OPO ₃ ^- M), and the like. In the above chemical formula, M represents a hydrogen atom, alkali metal, ammonium or organic ammonium. Among these, a carboxy group (--COOM) and its dissociated ionic form (--COO--) are preferred from the viewpoints of ease of introduction of an anionic group into the polymer skeleton and availability of monomers.

At least part of the anionic groups of the resin (A') are neutralized with a neutralizing agent (b) (hereinafter also referred to as "neutralizing agent (b)").
Examples of the neutralizing agent (b) include alkali metal compounds; basic compounds such as organic amine compounds and nitrogen-containing compounds such as ammonia. Among them, a strong base is preferable, and an alkali metal compound is more preferable, from the viewpoint of sufficiently expressing the electrostatic repulsive force due to neutralization and improving the dispersion stability of the pigment. Specific examples of alkali metals include lithium, sodium, potassium, rubidium and cesium. Among them, sodium and potassium are preferable, and sodium is more preferable, from the viewpoint of availability and expression of strong electrostatic repulsion by neutralization.
The alkali metal compound used as the neutralizing agent (b) is preferably an alkali metal hydroxide, and the alkali metal hydroxide can be used in the form of an aqueous solution from the viewpoint of sufficiently and uniformly promoting neutralization. preferable. The concentration of the aqueous alkali metal hydroxide solution is preferably 3% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, and preferably 50% by mass or less, more preferably 25% by mass. % or less.

Neutralization of the anionic group of the resin (A') is preferably carried out so that the pH is 7 or more and 11 or less.
The equivalent amount of the neutralizing agent (b) used is preferably 10 mol % or more, more preferably 20 mol % or more, and still more preferably It is 30 mol % or more, more preferably 40 mol % or more, and preferably 300 mol % or less, more preferably 200 mol % or less, still more preferably 150 mol % or less.
Here, the use equivalent of the neutralizing agent (b) can be obtained from the acid value and mass of the resin (A') before neutralization by the following formula. When the use equivalent of the neutralizing agent (b) is 100 mol% or less, it is synonymous with the degree of neutralization, and when the use equivalent of the neutralizing agent (b) exceeds 100 mol% in the following formula, It means that (b) is in excess with respect to the anionic groups of resin (A'), and the degree of neutralization of resin (A) at this time is regarded as 100 mol %.
Use equivalent (mol %) of neutralizing agent (b) = [{added mass (g) of neutralizing agent (b) / equivalent of neutralizing agent (b)} / [{acid value of resin (A') ( mgKOH/g)×mass of resin (A′) (g)}/(56×1,000)]]×100

From the viewpoint of improving the dispersion stability of the pigment, the resin (A) is preferably water-insoluble.
The term "water-insoluble" as used herein means that an aqueous dispersion obtained by dispersing the resin (A) in water to a concentration of 2×10 ⁻⁴ mass % does not become transparent. In the present invention, even if the aqueous dispersion looks transparent to the naked eye, it is judged to be water-insoluble when the Tyndall phenomenon is observed by observation with a laser beam or ordinary light.

The resin (A') contains a polyester structure, and examples thereof include polyester resins, styrene-acrylic resins containing a polyester structure, and polyurethane resins containing a polyester structure. Among them, a polyester resin is preferable from the viewpoint of improving the dispersion stability of the pigment.

(polyester resin)
The polyester resin used in the present invention is not particularly limited, but preferably contains a structural unit derived from an alcohol component and a structural unit derived from a carboxylic acid component, and is obtained by polycondensation of at least an alcohol component and a carboxylic acid component. .
The polyester resin preferably has a polyalkylene oxide structure, a so-called polyether structure, in its main chain from the viewpoint of improving the dispersion stability of the pigment and the storage stability and ejection properties of the ink. As a method for introducing a polyalkylene oxide structure into the main chain of a polyester resin, a method of polycondensation using a raw material monomer having a polyalkylene oxide structure is preferred. Examples of the raw material monomer include an alkylene oxide adduct of bisphenol A, which will be described later.

[Alcohol component]
The alcohol component, which is a raw material monomer constituting the polyester resin (hereinafter also referred to as a "raw material monomer of the polyester resin"), is an aromatic diol from the viewpoint of improving the dispersion stability of the pigment and the storage stability and ejection properties of the ink. It is preferred to include
The aromatic diol is preferably an alkylene oxide adduct of bisphenol A. Thereby, a polyalkylene oxide structure can also be introduced into the main chain of the polyester resin.
In the present invention, the alkylene oxide adduct of bisphenol A means the entire structure obtained by adding an oxyalkylene group to 2,2-bis(4-hydroxyphenyl)propane.
Specifically, the alkylene oxide adduct of bisphenol A is preferably a compound represented by the following general formula (I).

In general formula (I), both OR ¹ and R ² O are oxyalkylene groups, each independently preferably an oxyalkylene group having 1 to 4 carbon atoms, more preferably an oxyethylene group or oxypropylene is the base.
x and y correspond to the average number of added moles of alkylene oxide, and are each independently preferably 1 or more, more preferably 2 or more, and preferably 16 or less, more preferably 7 or less, and still more preferably 5 3 or less, and more preferably 3 or less. Furthermore, from the viewpoint of reactivity with the carboxylic acid component, the average value of the sum of x and y is preferably 2 or more, and is preferably 7 or less, more preferably 5 or less, and still more preferably 3 or less. .
Moreover, the x number of OR ¹ and the y number of R ² O may be the same or different, but from the viewpoint of improving adhesion to the substrate, they are preferably the same. The alkylene oxide adducts of bisphenol A may be used alone or in combination of two or more. The alkylene oxide adduct of bisphenol A is preferably a propylene oxide adduct of bisphenol A and an ethylene oxide adduct of bisphenol A, more preferably a propylene oxide adduct of bisphenol A.
The content of the alkylene oxide adduct of bisphenol A in the alcohol component, which is the raw material monomer of the polyester resin, is preferably 50 mol% or more from the viewpoint of improving the dispersion stability of the pigment and the storage stability and ejection properties of the ink. , more preferably 60 mol % or more, still more preferably 70 mol % or more, and preferably 100 mol % or less.

The alcohol component of the raw material monomer of the polyester resin may contain other alcohol components than the alkylene oxide adduct of bisphenol A.
Other alcohol components include, for example, linear or branched aliphatic diols such as ethylene glycol and propylene glycol (same as "1,2-propanediol"); alicyclic diols such as polyhydric alcohols having a valence or higher; hydrogenated bisphenol A or alkylene oxide adducts thereof (having 2 or more and 4 or less carbon atoms) (average addition mole number of 1 or more and 16 or less).
You may use the said alcohol component individually or in combination of 2 or more types.

[Carboxylic acid component]
A carboxylic acid component is used as the raw material monomer for the polyester resin in addition to the alcohol component.
The carboxylic acid component includes a carboxylic acid, an anhydride of the carboxylic acid, an alkyl (having 1 to 3 carbon atoms) ester of the carboxylic acid, and the like.
The carboxylic acid component is preferably an aromatic dicarboxylic acid, an aliphatic dicarboxylic acid, an alicyclic dicarboxylic acid, or a polyvalent carboxylic acid having a valence of 3 or more. And from the viewpoint of improving ejection properties, aromatic dicarboxylic acids and aliphatic dicarboxylic acids are more preferable, and aliphatic dicarboxylic acids are even more preferable.
The aromatic dicarboxylic acid is preferably phthalic acid, isophthalic acid or terephthalic acid, more preferably terephthalic acid.
Examples of aliphatic dicarboxylic acids include unsaturated aliphatic dicarboxylic acids and saturated aliphatic dicarboxylic acids. Saturated aliphatic dicarboxylic acids are preferred.
The unsaturated aliphatic dicarboxylic acid is preferably fumaric acid or maleic acid, more preferably fumaric acid, from the viewpoint of improving the reactivity between the carboxylic acid component and the alcohol component, and the storage stability and ejection properties of the ink.
Preferred saturated aliphatic dicarboxylic acids are adipic acid and succinic acid (succinic acid may be substituted with an alkyl group and/or an alkenyl group).
Preferred alicyclic dicarboxylic acids are cyclohexanedicarboxylic acid, decalinedicarboxylic acid, and tetrahydrophthalic acid.
Trivalent or higher polyvalent carboxylic acid is preferably trimellitic acid or pyromellitic acid.
The carboxylic acid component may be used alone or in combination of two or more.

[Method for producing polyester resin]
The polyester resin can be obtained by appropriately combining at least the alcohol component and the carboxylic acid component and subjecting them to polycondensation.
The polyester resin is produced, for example, by polycondensing the alcohol component and the carboxylic acid component in an inert gas atmosphere, optionally using an esterification catalyst, at a temperature of 180° C. or higher and 250° C. or lower. can do.
From the viewpoint of improving the dispersion stability of the pigment, the polyester resin preferably has a sharp molecular weight distribution and preferably undergoes polycondensation using an esterification catalyst.
Esterification catalysts include metal compounds such as tin catalysts, titanium catalysts, antimony trioxide, zinc acetate and germanium dioxide. A tin catalyst is preferable from the viewpoint of the reaction efficiency of the esterification reaction in the production of the polyester resin. The tin catalyst is preferably dibutyltin oxide, di(2-ethylhexanoate) tin (II), or a salt thereof, and more preferably di(2-ethylhexanoate) tin (II).
If necessary, an esterification co-catalyst such as 3,4,5-trihydroxybenzoic acid (gallic acid) may be used.
A radical polymerization inhibitor such as 4-tert-butylcatechol and hydroquinone may also be used in combination.

In the present invention, the resin (A) may have a crosslinked structure from the viewpoint of improving the dispersion stability of the pigment and the storage stability and ejection properties of the ink.
As a method for forming a crosslinked structure, a method (i ), the method (ii) of mixing the resin (A') or an anionic group of the resin (A) with a polyfunctional epoxy compound or a polyfunctional carbodiimide compound and heating to form a crosslinked structure. Among them, it is preferable to form a crosslinked structure by the method (i) from the viewpoint of ease of production.
From the viewpoint of improving the dispersion stability of the pigment and improving the storage stability and ejection properties of the ink, the trifunctional or higher monomer used in method (i) is preferably the above-described polycarboxylic acid or It is a hydric alcohol, more preferably a polyvalent carboxylic acid, still more preferably trimellitic acid, and still more preferably trimellitic anhydride.
From the viewpoint of improving the dispersion stability of the pigment, the content of the polyvalent carboxylic acid compound in the carboxylic acid component is preferably 1 mol% or more, more preferably 5 mol% or more, and still more preferably 10 mol% or more. Yes, preferably 30 mol % or less, more preferably 25 mol % or less, even more preferably 20 mol % or less, still more preferably 15 mol % or less.

The acid value of the resin (A') is preferably 5 mgKOH/g or more, more preferably 15 mgKOH/g or more, still more preferably 20 mgKOH, from the viewpoint of improving the dispersion stability of the pigment and the storage stability and ejection properties of the ink. /g, and preferably 40 mgKOH/g or less, more preferably 37 mgKOH/g or less, still more preferably 35 mgKOH/g or less.
The softening point of the resin (A′) is preferably 80° C. or higher, more preferably 85° C. or higher, and even more preferably 90° C. or higher, from the viewpoint of improving the dispersion stability of the pigment and the storage stability and ejection properties of the ink. and is preferably 170° C. or lower, more preferably 145° C. or lower, and even more preferably 125° C. or lower.
The glass transition temperature (Tg) of the resin (A′) is preferably 50° C. or higher, more preferably 55° C. or higher, from the viewpoint of improving the dispersion stability of the pigment and the storage stability and ejection properties of the ink. The temperature is preferably 95° C. or lower, more preferably 90° C. or lower, still more preferably 85° C. or lower, and even more preferably 80° C. or lower.
The weight-average molecular weight (Mw) of the resin (A') is preferably 5,000 or more, more preferably 7,500 or more, from the viewpoint of improving the dispersion stability of the pigment and the storage stability and ejection properties of the ink. More preferably 10,000 or more, still more preferably 12,500 or more, and preferably 100,000 or less, more preferably 75,000 or less, even more preferably 50,000 or less, still more preferably 30, 000 or less.
The acid value, softening point, glass transition temperature (Tg), and weight average molecular weight (Mw) of the resin (A') can all be measured by the methods described in Examples. A desired product can be obtained by appropriately adjusting the temperature and time of polycondensation.

(Mass ratio in pigment-containing resin composition [pigment/resin (A)])
In the pigment-containing resin composition, the mass ratio of the pigment to the resin (A) [pigment/resin (A)] is preferably 45 from the viewpoint of improving the dispersion stability of the pigment and the storage stability and ejection properties of the ink. /55 or more, more preferably 50/50 or more, still more preferably 55/45 or more, and preferably 75/25 or less, more preferably 70/30 or less, still more preferably 65/35 or less.

(Condition 2)
In the pigment-containing resin composition of the present invention, the content of volatile substances in the pigment-containing resin composition is 1% by mass or less (Condition 2). When the content of volatile substances is 1% by mass or less, the generation of microorganisms is suppressed and deterioration can be prevented. From this point of view, the content of volatile substances is preferably 0.8% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.3% by mass or less.
The content of volatile substances is measured by the method described in Examples.

(Condition 3)
In the pigment-containing resin composition of the present invention, the aqueous dispersion (α) obtained by dispersing the pigment-containing resin composition in water so that the concentration of the pigment-containing resin composition is 2 × 10 ^-4 mass%, measured by dynamic light scattering method The average particle size (hereinafter also referred to as “average particle size of the aqueous dispersion (α)”) determined by the cumulant method analysis is 0.5 μm or less (Condition 3). The average particle size of the aqueous dispersion (α) is an index showing the dispersibility of the pigment when the pigment-containing resin composition is dispersed in the dispersion or ink. The dispersion stability of the pigment is excellent, and coarse particles are reduced in the ink for inkjet recording containing the pigment-containing resin composition, and the storage stability and ejection properties of the ink are improved. From this point of view, the average particle size of the aqueous dispersion (α) is preferably 300 nm or less, more preferably 200 nm or less, still more preferably 180 nm or less, and even more preferably 170 nm or less.
The average particle size of the aqueous dispersion (α) is measured by the method described in Examples.

[Method for producing pigment-containing resin composition]
The pigment-containing resin composition of the present invention contains a pigment and a resin (A), and an aqueous pigment dispersion (D) in which the pigment is dispersed in an aqueous medium with the resin (A) (hereinafter referred to as "aqueous pigment dispersion (D) It is preferable to manufacture by a method of volatilizing and removing volatile substances from (also referred to as "). Among them, from the viewpoint of production efficiency, the method including the following step I and step II is more preferable.
Here, the "aqueous medium" means a liquid medium containing water as a main component.

Step I: A step of mixing and dispersing water, a pigment, a resin (A′), and a neutralizer (b) to obtain an aqueous pigment dispersion (D) Step II: The aqueous pigment dispersion obtained in Step I A step of drying (D) to obtain a pigment-containing resin composition having a volatile substance content of 1% by mass or less

(Process I)
Step I is a step of mixing and dispersing water, a pigment, a resin (A'), and a neutralizing agent (b) to obtain an aqueous pigment dispersion (D). As a result, at least part of the anionic groups of the resin (A') are neutralized with the neutralizing agent (b) to form the resin (A).
Although there is no particular limitation on the mixing order of each component in step I, resin (A′), organic solvent, water, neutralizing agent (b), and pigment are first mixed to prepare a pigment mixture, and It is preferable to obtain the water-based pigment dispersion (D) by applying shear stress.
The organic solvent used in step I is not particularly limited, but aliphatic alcohols having 1 to 3 carbon atoms, ketones, ethers, esters, etc. are preferable, and wettability to pigments and solubility of resin (A') , and from the viewpoint of improving the adsorptivity of the resin (A′) to the pigment, ketones having 4 to 8 carbon atoms are more preferable, methyl ethyl ketone and methyl isobutyl ketone are more preferable, and methyl ethyl ketone is even more preferable.
When the resin (A') is synthesized by a solution polymerization method, from the viewpoint of productivity, the organic solvent solution of the resin (A') may be used in step I without removing the organic solvent used in the polymerization reaction. good.

(Content of each component in the pigment mixture)
The content of each component in the pigment mixture is as follows from the viewpoint of improving productivity, pigment dispersion stability, and ink storage stability and ejection properties.
The content of the pigment in the pigment mixture is preferably 3% by mass or more, more preferably 5% by mass or more, still more preferably 10% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass. 20% by mass or less, more preferably 20% by mass or less.
The content of the resin (A′) in the pigment mixture is preferably 2% by mass or more, more preferably 5% by mass or more, still more preferably 7% by mass or more, and preferably 40% by mass or less, more preferably is 20% by mass or less, more preferably 15% by mass or less.
The content of the organic solvent in the pigment mixture is preferably 5% by mass or more, more preferably 7% by mass or more, still more preferably 10% by mass or more, and is preferably 35% by mass or less, more preferably 30% by mass. % or less, more preferably 25 mass % or less.
The water content in the pigment mixture is preferably 10% by mass or more, more preferably 20% by mass or more, and preferably 70% by mass or less, more preferably 60% by mass or less.

In the pigment mixture, the mass ratio of the pigment to the resin (A') [pigment/resin (A')] is preferably 45/55 or more, more preferably 50/50 or more, in order to improve the dispersion stability of the pigment. , more preferably 55/45 or more, and preferably 75/25 or less, more preferably 70/30 or less, and even more preferably 65/35 or less.

(Distributed processing)
There is no particular limitation on the method of applying shear stress to the pigment mixture in step I. It is possible to reduce the average particle size of the pigment mixture to a desired particle size using only one dispersion method. It is preferable to control the average particle size of the water-based pigment dispersion (D) to a desired particle size.
The temperature of the dispersion treatment in step I is preferably 0° C. or higher, and preferably 40° C. or lower, more preferably 25° C. or lower.
The time for the dispersion treatment in step I is preferably 1 hour or more, more preferably 2 hours or more, and preferably 30 hours or less, more preferably 25 hours or less.
When pre-dispersing the pigment mixture, generally used mixing and stirring devices such as anchor blades and disper blades, among which high-speed stirring and mixing devices are preferred.

Examples of means for imparting shear stress for this dispersion include kneaders such as roll mills and kneaders, high-pressure homogenizers such as Microfluidizer (manufactured by Microfluidics, trade name), and media dispersers such as paint shakers and bead mills. Commercially available media dispersers include Ultra Apex Mill (manufactured by Kotobuki Kogyo Co., Ltd., trade name) and Pico Mill (manufactured by Asada Iron Works Co., Ltd., trade name). A plurality of these devices can also be combined. Among these, it is preferable to use a high-pressure homogenizer from the viewpoint of making the pigment finer.
The dispersion treatment is preferably carried out by pre-dispersing with a disper or the like, followed by high-pressure dispersion treatment. In the high-pressure dispersion treatment, the pigment can be controlled to have a desired particle size by controlling the treatment pressure and the number of passes. Here, "high pressure dispersion" means dispersion at a dispersion pressure of 20 MPa or more.
Dispersion pressure is preferably 50 MPa or more, more preferably 100 MPa or more, still more preferably 120 MPa or more, and preferably 250 MPa or less, more preferably 200 MPa or less, from the viewpoint of making the pigment finer and dispersion processing efficiency. be.
The number of passes is preferably 3 or more, more preferably 7 or more, and is preferably 30 or less, more preferably 20 or less.

In step 1, after dispersing the pigment mixture, the organic solvent is preferably removed from the dispersed product by a known method. The organic solvent in the resulting aqueous pigment dispersion (D) is preferably substantially removed, but may remain as long as the object of the present invention is not impaired. The amount of residual organic solvent is preferably 0.1% by mass or less, more preferably 0.01% by mass or less.
In addition, if necessary, the dispersed material can be heated and stirred before distilling off the organic solvent.

The aqueous pigment dispersion (D) obtained in step 1 is obtained by dispersing the pigment in an aqueous medium containing water as a main component by means of the resin (A).
Here, the form of the water-based pigment dispersion (D) is not particularly limited, and particles are preferably formed from at least the pigment and the resin (A). Examples include a particle form in which the pigment is encapsulated in the resin (A), a particle form in which the pigment is uniformly dispersed in the resin (A), and a particle form in which the pigment is exposed on the particle surface of the resin (A). , including mixtures thereof.

(Average particle size of aqueous pigment dispersion (D))
The average particle size of the water-based pigment dispersion (D) is preferably 50 nm or more, more preferably 60 nm or more, and even more preferably 70 nm or more, from the viewpoint of improving the dispersion stability of the pigment, the storage stability of the ink, and the ejection property. and preferably 0.5 μm or less, more preferably 300 nm or less, even more preferably 200 nm or less, even more preferably 180 nm or less, and even more preferably 170 nm or less.
The average particle size of the water-based pigment dispersion (D) is a cumulant measured by a dynamic light scattering method by diluting the water-based pigment dispersion (D) with water so that the solid content concentration is 2 × 10 ^-4 % by mass. It means the average grain size obtained by the method analysis. Specifically, it is measured by the method described in Examples.

(Process II)
Step II is a step of drying the aqueous pigment dispersion (D) obtained in Step I to obtain a pigment-containing resin composition having a volatile substance content of 1% by mass or less.
The water-based pigment dispersion (D) obtained in step I contains water and volatile substances such as an organic solvent used as necessary. Therefore, in step II, the volatile substances contained in the aqueous pigment dispersion (D) are removed to obtain a solid pigment-containing resin composition having a volatile substance content of 1% by mass or less. The drying treatment is performed until the content of volatile substances in the pigment-containing resin composition is preferably 0.8% by mass or less, more preferably 0.5% by mass or less, and further preferably 0.3% by mass or less. preferably.
The content of volatile substances in the pigment-containing resin composition is measured by the method described in Examples.

Drying treatments include, for example, freeze drying, spray drying, hot air drying, blow drying, vacuum or reduced pressure drying, far-infrared heat drying, dehumidified air drying, and the like. Any commercially available device can be used for the drying treatment. Among these, freeze-drying or spray-drying is preferable from the viewpoint of the dispersion stability of the pigment and the ejection property of the ink, and from the viewpoint of suppressing thermal deterioration of the pigment and resin (A), and from the viewpoint of suppressing aggregation of the pigment. , lyophilization is preferred.
For spray drying, for example, the water-based pigment dispersion (D) is preferably sprayed in a spray drying apparatus and dried at an inlet temperature of 200° C. or lower and an outlet temperature of 110° C. or lower.
Freeze-drying is preferably performed by pre-freezing the water-based pigment dispersion (D), followed by primary drying and secondary drying.
Preliminary freezing is preferably rapid freezing at a temperature of -40°C or higher and -20°C or lower under normal pressure. Then, primary drying is performed to sublimate the ice in the pre-frozen material preferably under a vacuum of 0.1 Pa or more and 100 Pa or less at a temperature of −20° C. or more and −5° C. or less, and then a vacuum of 0.1 Pa or more and 100 Pa or less. It is preferable to perform secondary drying by raising the temperature to 20° C. or higher and 40° C. or lower.
Step II may further include a step of pulverizing the colored solid obtained after drying.

Since the pigment-containing resin composition of the present invention is excellent in the dispersion stability of the pigment, it is possible to obtain good printed matter, and it is suitable for use in printing inks such as flexographic printing inks, gravure printing inks, and inkjet recording inks. can be done. In addition, since the storage stability and dischargeability of the ink in ink jet recording are excellent, it is particularly preferable to use it for ink for ink jet recording.
Various additives such as surfactants, wetting agents, penetrants, viscosity modifiers, antifoaming agents, antifungal agents, anticorrosive agents, and ultraviolet absorbers may be added to the printing ink as necessary. can be done.
When the pigment-containing resin composition of the present invention is used as a printing ink, it is preferably produced by adding and mixing a liquid compound to the pigment-containing resin composition. Specific examples of liquid compounds include water, organic solvents, surfactants, disinfectants, and the like.

[Ink for inkjet recording]
The inkjet recording ink of the present invention (hereinafter also referred to as "inkjet recording ink") contains the pigment-containing resin composition.
The ink for inkjet recording may be water-based ink or non-water-based ink.
The term "aqueous ink" as used herein means that the mass ratio of water in the ink is the highest among liquid media.
The presence of the pigment and the resin (A) in the ink for inkjet recording includes a state in which the resin (A) is adsorbed to the pigment, a state in which the resin (A) contains the pigment, and a state in which the pigment is encapsulated (capsule). There are forms in which the resin (A) does not adsorb the pigment, and one type selected from these forms may be used alone, or two or more types may be mixed.

(water-based ink for inkjet recording)
A water-based ink for inkjet recording (hereinafter also referred to as "aqueous ink") contains the pigment-containing resin composition and water.
The content of the pigment in the water-based ink is preferably 1% by mass or more, more preferably 2% by mass or more, and still more preferably 4% by mass or more, from the viewpoint of improving print density. From the viewpoint of suppressing thickening of the ink and improving storage stability and ejection properties of the ink, the content is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 7% by mass or less.
The mass ratio of the pigment to the resin (A) in the water-based ink [pigment/resin (A)] is preferably 45/55 or more, more preferably 50/50, from the viewpoint of improving the storage stability and ejection properties of the ink. Above, more preferably 55/45 or more, preferably 75/25 or less, more preferably 70/30 or less, still more preferably 65/35 or less.
The water content in the water-based ink is preferably 20% by mass or more, more preferably 30% by mass or more, still more preferably 40% by mass or more, and preferably 70% by mass or less, more preferably 65% by mass. 60% by mass or less, more preferably 60% by mass or less.

From the viewpoint of suppressing evaporation of the ink medium and improving the storage stability and ejection properties of the ink, the water-based ink preferably contains a water-soluble organic solvent (B) in addition to water as the liquid medium.
The water-soluble organic solvent (B) preferably contains one or more organic solvents having a boiling point of 90° C. or higher.
The weighted average boiling point of the water-soluble organic solvent (B) contained in the ink is preferably 150° C. or higher, more preferably 180° C. or higher, and is preferably 250° C. or lower, more preferably 240° C. or lower. It is more preferably 220° C. or lower, still more preferably 200° C. or lower.

Examples of the water-soluble organic solvent (B) include polyhydric alcohols, polyhydric alcohol alkyl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds. Among these, one or more selected from polyhydric alcohols and polyhydric alcohol alkyl ethers are preferable, and ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, trimethylolpropane, diethylene glycol monobutyl ether, and diethylene glycol. One or more selected from diethyl ether is more preferable, and one or more selected from propylene glycol, diethylene glycol monobutyl ether, glycerin, triethylene glycol, and trimethylolpropane is even more preferable.
The content of the water-soluble organic solvent (B) in the water-based ink is preferably 10% by mass or more, more preferably 20% by mass or more, and still more preferably 30% by mass, from the viewpoint of improving the storage stability and ejection properties of the ink. % or more, and preferably 50% by mass or less, more preferably 47% by mass or less, and even more preferably 43% by mass or less.

The water-based ink preferably contains a surfactant (C) from the viewpoint of improving the wetting and spreading properties of the ink on the printing medium. Surfactants (C) include nonionic surfactants, anionic surfactants, amphoteric surfactants, silicone surfactants, fluorine surfactants, and the like. Among them, nonionic surfactants are preferred.
Nonionic surfactants include polyoxyalkylene alkyl ether surfactants, acetylene glycol surfactants, polyhydric alcohol surfactants, fatty acid alkanolamides, silicone surfactants, and fluorine surfactants. mentioned. Among these, one or more selected from polyoxyalkylene alkyl ether surfactants, acetylene glycol surfactants, and silicone surfactants are preferred, and silicone surfactants are more preferred.
The content of the surfactant (C) in the water-based ink is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably, from the viewpoint of improving the wetting and spreading properties of the ink on the printing medium. is 0.3% by mass or more, and preferably 3% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less.

(Curable ink for inkjet recording)
The ink for inkjet recording may be a curable ink for inkjet recording (hereinafter also referred to as “curable ink”) that is cured by irradiation with active energy rays such as ultraviolet rays and electron beams.
In the case of a curable ink, the resin (A) of the pigment-containing resin composition preferably has the above-described crosslinked structure from the viewpoints of pigment dispersion stability, ink storage stability, and ejection properties.
The content of the pigment in the curable ink is preferably 1% by mass or more, more preferably 2% by mass or more, and still more preferably 2.5% by mass or more, from the viewpoint of improving print density. From the viewpoint of suppressing thickening and improving the storage stability and ejection properties of the ink, the content is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less.
The mass ratio of the pigment to the resin (A) in the curable ink [pigment/resin (A)] is preferably 45/55 or more, more preferably 50/50, from the viewpoint of improving the storage stability and ejection properties of the ink. 50 or more, more preferably 55/45 or more, and preferably 75/25 or less, more preferably 70/30 or less, and even more preferably 65/35 or less.

The curable ink contains a pigment-containing resin composition and an active energy ray polymerizable compound (E) (hereinafter also referred to as “polymerizable compound (E)”), and the polymerizable compound (E) is liquid. preferable. The polymerizable compound (E) is preferably liquid at 25° C., and the viscosity of the polymerizable compound (E) at 25° C. is preferably 5 mPa·s or more, more preferably 10 mPa·s or more, from the viewpoint of ink ejection properties. s or more, more preferably 15 mPa·s or more, and preferably 35 mPa·s or less, more preferably 30 mPa·s or less, still more preferably 25 mPa·s or less. The viscosity of the polymerizable compound (E) can be measured using an E-type viscometer.

The polymerizable compound (E) is a compound having a reactive group capable of being polymerized by irradiation with active energy rays (hereinafter also referred to as “reactive group”). The term “reactive group” means a functional group that undergoes a curing reaction through direct polymerization by irradiation with active energy rays such as ultraviolet rays or by the action of a photopolymerization initiator. Examples of the reactive group include functional groups having an ethylenically unsaturated bond such as an epoxy group, an acryloyl group, a methacryloyl group, a vinyl group and an allyl group. From the viewpoint of storage stability and ejection property of the ink, the polymerizable compound (E) contains, in addition to the above reactive groups, a hydroxyl group, a polyalkyleneoxy group, an ether group, an ionic group, an amide group, an amino group, and the like. It preferably has one or more functional groups.
The polymerizable compound (E) is preferably one or more selected from epoxy group-containing compounds (E1) and ethylenically unsaturated bond-containing compounds (E2) from the viewpoint of ink storage stability and ejection properties. Combination of the epoxy group-containing compound (E1) and the ethylenically unsaturated bond-containing compound (E2) is preferred.

[Epoxy group-containing compound (E1)]
The epoxy group-containing compound (E1) is a compound containing two or more epoxy groups in the molecule, and is preferably an epoxy group-containing monomer or epoxy resin.
The epoxy equivalent of the epoxy group-containing compound (E1) is preferably 90 or more, more preferably 100 or more, still more preferably 110 or more, and preferably 300 or less, more preferably 200, from the viewpoint of ink curability. 150 or less, more preferably 150 or less.

Examples of the epoxy group-containing compound (E1) include linear, branched or alicyclic aliphatic epoxy resins; and polycyclic aromatic epoxy resins such as bisphenol F type epoxy resins and bisphenol A type epoxy resins.
Examples of epoxy group-containing compounds (E1) include 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, neopentyl glycol diglycidyl ether, and cyclohexanedimethanol diglycidyl ether. , bisphenol F diglycidyl ether and the like.
Commercial products of the epoxy group-containing compound (E1) include HELOXY 48, HELOXY 67, HELOXY 68, and HELOXY 107 (manufactured by Hexion Specialty Chemicals Inc.). Among them, neopentyl glycol diglycidyl ether is preferred.

[Ethylenically unsaturated bond-containing compound (E2)]
The ethylenically unsaturated bond-containing compound (E2) is a compound having a functional group having one or more ethylenically unsaturated bonds in the molecule. The functional group having an ethylenically unsaturated bond is preferably one or more selected from acryloyl groups and methacryloyl groups.
The number of functional groups having an ethylenically unsaturated bond in the ethylenically unsaturated bond-containing compound (E2) is preferably 1 or more from the viewpoint of the dispersion stability of the pigment and the storage stability and ejection properties of the ink, and It is preferably 6 or less, more preferably 4 or less, even more preferably 3 or less, and even more preferably 2 or less.
The molecular weight of the ethylenically unsaturated bond-containing compound (E2) is preferably 50 or more and preferably 2,000 or less.

Examples of the ethylenically unsaturated bond-containing compound (E2) include hydroxyalkyl (meth) acrylate; alkylene oxide-modified glycerin di (meth) acrylate; alkylene oxide-modified glycerin tri (meth) acrylate; polyethylene glycol (n = 2 to 30, n represents the average number of added moles of ethylene oxide.In this specification, n represents the average number of added moles of the alkylene oxide.) (Meth) acrylate; Alkoxypolyalkylene glycol (meth)acrylates; phenoxy (ethylene glycol/propylene glycol copolymer) (n=1-30, ethylene glycol therein: n=1-29) (meth)acrylates; alkylene oxide adducts of allyl alcohol (n = 1 to 30); trimethylolpropane triacrylate and its alkylene oxide adduct (n = 1 to 30); pentaerythritol (meth)acrylate and its alkylene oxide adduct (n = 1 to 30); N, N - (meth)acrylamides such as dimethylaminoethyl (meth)acrylate, N,N-dimethyl (meth)acrylamide, N-methoxymethyl (meth)acrylamide, N-hydroxymethyl (meth)acrylamide; acryloylmorpholine; acrylic-modified silicones etc. The ethylenically unsaturated bond-containing compound (E2) may be used alone or in combination of two or more.
In addition, in this specification, "(meth)acrylate" means at least 1 sort(s) chosen from an acrylate and a methacrylate.

The ethylenically unsaturated bond-containing compound (E2) preferably has one or more selected from a hydroxy group and a polyalkyleneoxy group, from the viewpoint of the dispersion stability of the pigment and the storage stability and ejection properties of the ink ( meth)acrylates, more preferably one or more selected from hydroxy group-containing (meth)acrylates obtained by reacting acrylic acid with alkylcarboxylic acid glycidyl esters and alkylene oxide-modified glycerin di(meth)acrylates; Combination of hydroxy group-containing (meth)acrylate and alkylene oxide-modified glycerine di(meth)acrylate is preferred.

The content of the ethylenically unsaturated bond-containing compound (E2) in the curable ink is preferably 5% by mass or more, more preferably 10% by mass or more, and still more preferably 15% by mass, from the viewpoint of storage stability and ejection properties. % or more, and preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less.

The curable ink preferably further contains a polymerization initiator from the viewpoint of promoting curing by irradiation with active energy rays. The polymerization initiator is preferably a photopolymerization initiator that generates cations or radicals upon exposure to active energy rays.
Examples of photocationic polymerization initiators include aromatic iodonium salts and aromatic sulfonium salts.
Examples of photoradical polymerization initiators include acetophenones, benzoyls, benzophenones, ketals, anthraquinones, thioxanthones, azo compounds, peroxides, 2,3-dialkylsion compounds, disulfide compounds, and thiuram compounds. and fluoroamine compounds.
Among them, when the epoxy group-containing compound (E1) and the ethylenically unsaturated bond-containing compound (E2) are used in combination, a photocationic polymerization initiator and a photoradical polymerization initiator are used in combination from the viewpoint of promoting curing. is preferred.

The content of the photopolymerization initiator in the curable ink is preferably 1% by mass or more, more preferably 3% by mass or more, and still more preferably 5% by mass or more, from the viewpoint of storage stability and ejection properties of the ink. , and preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less.

The curable ink may contain an aqueous medium containing water as a main component. Components other than water that can be contained in the aqueous medium include, for example, alkyl alcohols having 1 to 5 carbon atoms; dialkyl ketones having 3 to 5 total carbon atoms such as acetone and methyl ethyl ketone; and cyclic ethers such as tetrahydrofuran. Dissolving organic solvents are included. The boiling point of the organic solvent is preferably 150° C. or lower, more preferably 130° C. or lower, and even more preferably 110° C. or lower.
The content of the aqueous medium in the curable ink is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less.

[Method for producing ink for inkjet recording]
The inkjet recording ink is preferably produced by a method including Step III below in addition to Step I and Step II described above.
Step III: A step of mixing the pigment-containing resin composition obtained in Step II with a liquid compound to obtain an inkjet recording ink. (C), a polymerizable compound (E), a polymerization initiator, a disinfectant, and the like. The liquid compounds may be used singly or in combination of two or more.
In the case of water-based ink, the liquid compound is preferably water, more preferably water and a water-soluble organic solvent (B).
In the case of curable ink, the liquid compound is the polymerizable compound (E), and preferably further contains a polymerization initiator.
Any known method can be used as the mixing method in step III.
The mixing temperature is preferably 5°C or higher, more preferably 10°C or higher, and preferably 40°C or lower.
When the polymerization initiator, surfactant, bactericide, or moisturizing agent is solid, it is preferable to dissolve it in water, an organic solvent, or the like to make it into a liquid state before mixing it with the pigment-containing resin composition.

(Average particle size of inkjet recording ink)
The average particle diameter of the ink for inkjet recording determined by the cumulant method analysis measured by the dynamic light scattering method is preferably 200 nm or less, more preferably 180 nm or less, and It is preferably 170 nm or less. The average particle size is the average particle size obtained by diluting the ink for inkjet recording with water so that the solid content concentration is 2×10 ⁻⁴ mass %, and measuring it by the cumulant method analysis by the dynamic light scattering method. be. Specifically, it can be measured by the method described in Examples.

As a method for diluting the ink for inkjet recording with water, in the case of water-based ink, the water-based ink may be diluted with water so that the solid content concentration becomes 2×10 ⁻⁴ mass %.
In the case of a curable ink, as the first stage of dilution, the curable ink is diluted with an organic solvent used for water-based ink so that the solid content concentration is 1×10 ⁻² mass % or more and 20 mass % or less, Furthermore, it is preferable to dilute with water until the solid content concentration reaches 2×10 ⁻⁴ mass % as the second stage of dilution. In the curable ink diluted with water, water accounts for the largest proportion of the liquid medium, so the numerical value of water is used as the refractive index of the dispersion solvent used in the measurement of the average particle diameter of the curable ink by the dynamic light scattering method.

(Physical properties of water-based ink for inkjet recording)
The viscosity of the water-based ink for inkjet recording at 32° C. is preferably 2 mPa·s or more, more preferably 3 mPa·s or more, and still more preferably 5 mPa·s or more, from the viewpoint of improving the storage stability and ejection properties of the ink. , and preferably 12 mPa·s or less, more preferably 9 mPa·s or less, and still more preferably 7 mPa·s or less. The viscosity of the aqueous ink can be measured using an E-type viscometer.
From the viewpoint of improving the storage stability of the ink, the pH of the water-based ink for inkjet recording is preferably 7 or higher, more preferably 7.2 or higher, and still more preferably 7.5 or higher. Also, from the viewpoint of member resistance and skin irritation, the pH is preferably 11 or less, more preferably 10 or less, and even more preferably 9.5 or less.

[Inkjet recording method]
The ink for inkjet recording can be loaded into a known inkjet recording apparatus and ejected as ink droplets onto a print medium to record an image or the like.
There are thermal type and piezo type ink jet recording apparatuses, and it is more preferable to use the ink for piezo type ink jet recording.
Usable print media include highly absorbent plain paper, low absorbent coated paper and resin film. Examples of coated paper include general-purpose glossy paper and multicolor foam gloss paper, and examples of resin films include polyester film, polyvinyl chloride film, polypropylene film, polyethylene film, and the like.

In the following Production Examples, Examples and Comparative Examples, "parts" and "%" are "mass parts" and "mass%" unless otherwise specified.

(1) Acid value of resin (A') Except for changing the measuring solvent from a mixed solvent of ethanol and ether to a mixed solvent of acetone and toluene [acetone:toluene = 1:1 (volume ratio)]. , measured according to the neutralization titration method described in JIS K0070-1992.

(2) Softening point of resin (A') Using a flow tester "CFT-500D" (manufactured by Shimadzu Corporation), a 1 g sample is heated at a temperature increase rate of 6 ° C./min, and a plunger is used to soften the temperature to 1.96 MPa. and extruded from a nozzle with a diameter of 1 mm and a length of 1 mm. The amount of plunger depression of the flow tester was plotted against the temperature, and the softening point was defined as the temperature at which half of the sample flowed out.

(3) Glass transition temperature (Tg) of resin (A')
The sample was heated to 200°C using a differential scanning calorimeter (manufactured by Perkin Elmer, trade name: Pyris 6 DSC) and cooled from that temperature to 0°C at a cooling rate of 10°C/min at a heating rate of 10°C/min. The glass transition temperature (Tg) was defined as the temperature at the intersection of the extension of the baseline below the maximum endothermic peak temperature and the tangential line showing the maximum slope from the rising portion of the peak to the apex of the peak.

(4) Weight average molecular weight (Mw) and molecular weight distribution (Mw/Mn) of resin (A')
(4-1) Preparation of sample solution Resin (A') was dissolved in chloroform (reagent manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) so that the concentration was 0.5 g/100 mL. Next, this solution was filtered using a fluororesin filter “FP-200” (manufactured by Sumitomo Electric Industries, Ltd.) with a pore size of 2 μm to remove undissolved components to obtain a sample solution.
(4-2) Molecular Weight Measurement Tetrahydrofuran (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd., for high-performance liquid chromatography) was allowed to flow as a dissolving solution at a flow rate of 1 mL per minute, and the column was stabilized in a constant temperature bath at 40°C. 100 μL of the sample solution was injected thereinto and measured. The weight-average molecular weight and molecular weight distribution of the sample were calculated based on a previously prepared calibration curve. The calibration curve was prepared using ^six types of monodisperse polystyrene [ ^monodisperse polystyrene manufactured by ^Tosoh Corporation; ^Monodisperse polystyrene manufactured by ^Science Co. ^, Ltd.;
Measuring device: "CO-8010" (manufactured by Tosoh Corporation)
Analysis column: "GMHXL" + "G3000HXL" (manufactured by Tosoh Corporation)

(5) Measurement of average particle size of water-based pigment dispersion (D) Using a laser particle analysis system "ELS-8000" (manufactured by Otsuka Electronics Co., Ltd.), the particle size is measured by a dynamic light scattering method, and a cumulant method. Calculated by analysis. The measurement conditions were a temperature of 25° C., an angle between the incident light and the detector of 90°, and 100 integration times, and the refractive index of water (1.333) was input as the refractive index of the dispersion solvent. For the measurement sample, the water-based pigment dispersion (D) was weighed into a screw tube (No. 5 manufactured by Maruem Co., Ltd.), water was added so that the solid content concentration was 2 × 10 ^-4 % by mass, and a magnetic stirrer was added. used and stirred at 25° C. for 1 hour.

(6) Measurement of solid content concentration Using an infrared moisture meter "FD-230" (manufactured by Ketsuto Kagaku Kenkyusho Co., Ltd.), 5 g of the measurement sample is dried at 150 ° C., measurement mode 96 (monitoring time 2.5 minutes / fluctuation After drying under the condition of width 0.05%), the water content (%) of the measurement sample was measured, and the solid content concentration was calculated by the following formula.
Solid content concentration (%) = 100 - (moisture content (%) of measurement sample)

(7) Measurement of Volatile Substance Content 10.0 g of the pigment-containing resin composition was weighed into a glass petri dish having a diameter of 10 mm, and the mass was measured. After that, it was left at 40° C. for 12 hours, and the mass was measured again. The content of volatile substances was obtained by dividing the difference in mass before and after standing by the sample mass before standing.

(Production of polyester resins A'1 to A'2)
Production Examples 1-2
Raw material monomers (alcohol component and carboxylic acid component) for polyester resin, esterification catalyst, and esterification co-catalyst are mixed in the proportions shown in Table 1, and equipped with a thermometer, stirring device, flow-down condenser, and nitrogen introduction pipe. Put it in a 10 L four-necked flask and use a mantle heater in a nitrogen atmosphere to react at 210 ° C. for 10 hours. to obtain polyester resins A'1 and A'2. Table 1 shows the physical properties of the obtained polyester resins A'1 and A'2.

<Production of Pigment-Containing Resin Composition>
Example 1-1
(Process I)
In a container with an internal volume of 2 L, 66.7 g of polyester resin A'1 as resin (A') is dissolved in 156.4 g of methyl ethyl ketone, and 5N aqueous sodium hydroxide solution (Fujifilm Wako Pure Yaku Co., Ltd. for titration) and 430 g of ion-exchanged water are added, and the degree of neutralization with sodium hydroxide is adjusted to 85 mol% with respect to the acid value of the polyester resin. The mixture was stirred and mixed for 15 minutes at 2,000 r/min using a disper blade at a temperature of 0°C or lower.
Subsequently, 100 g of a black pigment (carbon black, trade name: MONARCH 717, manufactured by Cabot Corporation) was added to obtain a pigment mixture, and then stirred at 7,000 r/min for 2 hours at 10°C or higher and 15°C or lower using a disper blade. Mixed and pre-dispersed.
The resulting preliminary dispersion was filtered through 150 mesh, diluted by adding 36.1 g of ion-exchanged water, and then using a microfluidizer "M-110EH-30XP" (trade name, manufactured by Microfluidics, a high-pressure homogenizer). , After 15 passes of dispersion treatment at a pressure of 150 MPa, the entire amount was placed in a 2 L eggplant flask, ion-exchanged water was added so that the solid content concentration was 16%, and a rotary distillation apparatus "rotary evaporator N-1000S" ( (manufactured by Tokyo Rikakikai Co., Ltd.), the organic solvent was removed by maintaining a pressure of 0.09 MPa (abs) for 3 hours in a hot bath adjusted to 32° C. at a rotational speed of 50 r/min. Furthermore, the hot bath was adjusted to 62° C., the pressure was lowered to 0.07 MPa (abs), and water was distilled off until the solid concentration reached 25% to obtain a concentrate.
The resulting concentrate was put into a 500 mL angle rotor and centrifuged at 3,660 r/min for 20 minutes using a high-speed cooling centrifuge "himac CR22G" (manufactured by Hitachi Koki Co., Ltd., set temperature 20 ° C.), The liquid layer portion was filtered through a membrane filter "Minisart" (manufactured by Sartorius) having a pore size of 5 μm to obtain an aqueous pigment dispersion (D1).

(Process II)
Aqueous pigment dispersion (D1) obtained in step I in a dry chamber (model: DRC-1000, manufactured by Tokyo Rikaki Co., Ltd.) connected to a freeze dryer (model: FDU-2110, manufactured by Tokyo Rikaki Co., Ltd.) 100 g was added, pre-frozen (normal pressure, −25° C., 1 hour), primary drying (5 Pa, −10° C., 9 hours), secondary drying (5 Pa, 25° C., 5 hours), and freeze-drying. . The resulting colored solid was pulverized to obtain a pigment-containing resin composition 1.

Example 1-2
Pigment-containing resin composition 2 was obtained in the same manner as in Example 1-1 except that polyester resin A'2 was used instead of polyester resin A'1 to obtain an aqueous pigment dispersion (D2) in the same manner. rice field.

Example 1-3
In Example 1-2, instead of 75 g of black pigment, 75 g of cyan pigment (PB15:3, trade name: CFB6338JC, manufactured by Dainichi Seika Kogyo Co., Ltd.) was used in the same manner to obtain an aqueous pigment dispersion (D3). A pigment-containing resin composition 3 was obtained in the same manner except that

Examples 1-4
In Example 1-2, instead of 75 g of black pigment, 75 g of magenta pigment (PR150, trade name: Fuji Fast Carmine 522-1D, manufactured by Fuji Pigment Co., Ltd.) was used to prepare an aqueous pigment dispersion (D4) in the same manner. A pigment-containing resin composition 4 was obtained in the same manner as above.

Examples 1-5
Same as Example 1-2, except that 75 g of a yellow pigment (PY155, trade name: Inkjet Yellow 4GC, manufactured by Clariant) was used instead of 75 g of the black pigment, and an aqueous pigment dispersion (D5) was obtained in the same manner. Then, a pigment-containing resin composition 5 was obtained.

Comparative Example 1-1
In Example 1-1, a styrene-acrylic copolymer (trade name: JONCRYL 690, weight average molecular weight: 16,500, acid value: 240, A pigment-containing resin composition C1 was obtained in the same manner, except that an aqueous pigment dispersion (DC1) was obtained in the same manner using BASF Corporation).

Comparative Example 1-2
In Comparative Example 1-1, 75 g of a cyan pigment (PB15:3, trade name: CFB6338JC, manufactured by Dainichiseika Kogyo Co., Ltd.) was used instead of 75 g of the black pigment, and a water-based pigment dispersion (DC2) was obtained in the same manner. Pigment-containing resin composition C2 was obtained in the same manner as above.

Comparative Example 1-3
In Comparative Example 1-1, an aqueous pigment dispersion (DC3) was prepared in the same manner using 75 g of a magenta pigment (PR150, trade name: Fuji Fast Carmine 522-1D, manufactured by Fuji Pigment Co., Ltd.) instead of 75 g of the black pigment. A pigment-containing resin composition C3 was obtained in the same manner as above, except for the above.

Comparative Example 1-4
The same procedure as in Comparative Example 1-1 except that 75 g of a yellow pigment (PY155, trade name: Inkjet Yellow 4GC, manufactured by Clariant) was used instead of 75 g of the black pigment to obtain an aqueous pigment dispersion (DC4). to obtain a pigment-containing resin composition C4.

(Measurement of average particle size of aqueous dispersion (α) by dynamic light scattering method)
Each pigment-containing resin composition obtained in Examples and Comparative Examples and water were weighed into a screw tube (model number: No. 5, manufactured by Maruem Co., Ltd.) so that the solid content concentration was 2×10 ⁻⁴ %. and stirred at 25° C. for 1 hour using a magnetic stirrer to obtain each aqueous dispersion (α). Using the obtained aqueous dispersion (α), a laser particle analysis system "ELS-8000" (manufactured by Otsuka Electronics Co., Ltd.) is used to measure the particle size by the dynamic light scattering method, and the average is obtained by the cumulant method analysis. Particle size was calculated. The measurement conditions were a temperature of 25° C., an angle between the incident light and the detector of 90°, and 100 integration times, and the refractive index of water (1.333) was input as the refractive index of the dispersion solvent. The smaller the average particle size of the water dispersion (α), the better the dispersibility of the pigment. Table 2 shows the results.

In addition, each notation in Table 2 is as follows.
CB: Black pigment (carbon black, trade name: MONARCH 717, manufactured by Cabot)
PB15:3: Cyan pigment (PB15:3, trade name: CFB6338JC, manufactured by Dainichiseika Kogyo Co., Ltd.)
PR150: Magenta pigment (PR150, trade name: Fuji Fast Carmine 522-1D, manufactured by Fuji Pigment Co., Ltd.)
PY155: yellow pigment (PY155, trade name: Inkjet Yellow 4GC, manufactured by Clariant)

<Production of water-based ink for inkjet recording>
Example 2-1
(Process III)
Pigment-containing resin composition 1 obtained in Example 1-1 8.3 g, propylene glycol (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., reagent) 35.0 g, diethylene glycol monobutyl ether (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., Reagent) 5.0 g, silicone surfactant (trade name: KF6011, manufactured by Shin-Etsu Chemical Co., Ltd., polyether-modified silicone) 0.50 g, and ion-exchanged water 51.2 g were added to a glass container and stirred at room temperature with a magnetic stirrer. After stirring for 1 hour, the mixture was filtered with a 25 mL needleless syringe (manufactured by Terumo Corporation) equipped with a 5 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, manufactured by Fujifilm Corporation), and the water for inkjet recording was A system ink I1 was obtained.

Examples 2-2 to 2-5, and Comparative Examples 2-1 and 2-2
In Example 2-1, instead of the pigment-containing resin composition 1 obtained in Example 1-1, the pigments obtained in Examples 1-2 to 1-5 and Comparative Examples 1-1 and 1-2 Inkjet recording water-based inks I2 to I5 and IC1 and IC2 were obtained in the same manner as in Example 2-1, except that resin compositions 2 to 5 and C1 and C2 were used.

<Production of UV curable ink for inkjet recording>
Example 2-6
(Process III)
4.2 g of the pigment-containing resin composition 2 obtained in Example 1-2, 60 g of neopentyl glycol diglycidyl ether (trade name: Heloxy 68, manufactured by Hexion Specialty Chemicals Inc.) as the polymerizable compound (E1), and polymerization As a chemical compound (E2), 8.3 g of tripropylene glycol diacrylate (manufactured by Tokyo Chemical Industry Co., Ltd., reagent) and a reaction product of glycidyl ester of acrylic acid and versatic acid 10 (trade name: ACE, Hexion Specialty Chemicals Inc. Co., Ltd.) 17.4 g, 4.0 g of phenyl-p-octyloxyphenyl-iodonium hexafluoroantimonate (trade name: UVACURE 1600, manufactured by Cytec Surface Specialties) as a photocationic polymerization initiator, and methylbenzoyl as a photoradical polymerization initiator. Formate (trade name: Genocure MBF, manufactured by Rahn Corporation) 4.0 g and isopropylthioxanthone (trade name: Esacure ITX (SR1124), manufactured by Sartomer Company, Inc.) 1.5 g, 4-methoxyphenol as a polymerization inhibitor (manufactured by Tokyo Chemical Industry Co., Ltd., reagent) 0.05 g, polyacrylate surface conditioner (trade name: BYK-361N, manufactured by BYK-Chemie, Wallingford, CT) 0.05 g, silicone antifoaming agent (BYK- 080A, BYK-Chemie, Wallingford, Conn.) 0.5 g was added to a brown glass container, stirred with a magnetic stirrer at room temperature for 1 hour, and filtered through a 5 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, Fuji (manufactured by Terumo Corporation) to which a 25 mL needleless syringe (manufactured by Terumo Corporation) was attached to obtain an ultraviolet curable ink I6 for inkjet recording.

Examples 2-7 to 2-9, and Comparative Examples 2-3 and 2-4
In Example 2-6, instead of the pigment-containing resin composition 2, Examples 1-3 to 1-5, and the pigment-containing resin compositions 3 to 5 obtained in Comparative Examples 1-1 and 1-2, and Inkjet recording ultraviolet curable inks I7 to I9 and IC3 and IC4 were obtained in the same manner as in Examples 2-6, except that C1 and C2 were used.

<Evaluation of inkjet recording ink>
The average particle size of the inks obtained in Examples and Comparative Examples was measured by the following procedure, and the average particle size of the ink and the average particle size of the aqueous dispersion (α) of the pigment-containing resin composition used in the ink were determined. A particle size change rate (=[[average particle size of ink]/[average particle size of aqueous dispersion (α)]]), which is a ratio to the diameter, was calculated. If the particle size change rate is 120% or less, it is difficult to cause a change in color during printing, and the dispersion stability of the pigment is judged to be "stable". It was judged that the dispersion stability of the pigment was "unstable" because it easily changed. Table 3 shows the results.

(Measurement of average particle size of inkjet recording ink)
Each of the inks obtained in Examples and Comparative Examples was allowed to stand at room temperature for 12 hours. After that, it is weighed into a screw tube (model number: No. 5, manufactured by Maruem Co., Ltd.), water is added so that the solid content concentration becomes 2×10 ⁻⁴ %, and the mixture is stirred at 5° C. for 1 hour using a magnetic stirrer, The particle size was measured by the dynamic light scattering method using a laser particle analysis system "ELS-8000" (manufactured by Otsuka Electronics Co., Ltd.), and the average particle size was calculated by the cumulant method analysis.
The measurement conditions were a temperature of 25° C., an angle between the incident light and the detector of 90°, and 100 integration times, and the refractive index of water (1.333) was input as the refractive index of the dispersion solvent.
In the case of a curable ink, the first stage dilution is performed using propylene glycol so that the solid content concentration becomes 2×10 ⁻² mass %, and then water is used to reduce the solid content concentration to 2×. A second dilution of 10 ^-4 % was used as a measurement sample.

From Table 3, in Examples 2-1 to 2-9, the pigment-containing resin compositions 1 to 5 that satisfy the conditions 1 to 3 are used. It can be seen that the characteristics are excellent.
On the other hand, in Comparative Examples 2-1 to 2-4, a styrene-acrylic copolymer was used as the dispersing resin, and the pigment-containing resin compositions C1 and C2 did not satisfy Condition 1. The particle size change rate is higher than that of inks I2 and I3, and the particle size change rate is significantly higher than that of curable inks I6 and I7 using the same pigment type, indicating that the dispersion stability of the pigment is inferior. I understand.

Claims (7)

A pigment-containing resin composition containing a pigment and a resin (A), satisfying conditions 1 to 3 below,
Condition 1: The resin (A) has an anionic group, and at least part of the anionic group of the resin (A') containing a polyester structure is neutralized with the neutralizing agent (b).
Condition 2: The content of volatile substances in the pigment-containing resin composition is 1% by mass or less.
Condition 3: A water dispersion (α) obtained by dispersing the pigment-containing resin composition in water so that the concentration of the pigment-containing resin composition is 2 × 10 ^-4 % by mass, measured by dynamic light scattering method. The average particle diameter obtained by cumulant method analysis is 0.5 μm or less.
Resin (A') is a polyester resin containing a structural unit derived from an alcohol component and a structural unit derived from a carboxylic acid component,
the alcohol component comprises an alkylene oxide adduct of bisphenol A;
The content of the alkylene oxide adduct of bisphenol A in the alcohol component is 50 mol% or more and 100 mol% or less,
The weight average molecular weight (Mw) of the resin (A') is 5,000 or more and 100,000 or less,
A pigment-containing resin composition, wherein the mass ratio of the pigment to the resin (A) [pigment/resin (A)] is 45/55 or more and 75/25 or less. 2. The pigment-containing resin composition according to claim 1, wherein the resin (A') has an acid value of 5 mgKOH/g or more and 40 mgKOH/g or less . 3. The pigment-containing resin composition according to claim 1 , wherein the neutralizing agent (b) is an alkali metal compound . An inkjet recording ink containing the pigment-containing resin composition according to any one of claims 1 to 3. 4. A method for producing a pigment-containing resin composition according to any one of claims 1 to 3, comprising the following Step I and Step II.
Step I: A step of mixing and dispersing water, a pigment, a resin (A′), and a neutralizer (b) to obtain an aqueous pigment dispersion (D) Step II: The aqueous pigment dispersion obtained in Step I A step of drying (D) to obtain a pigment-containing resin composition having a volatile substance content of 1% by mass or less, wherein the aqueous pigment dispersion (D) contains a pigment and a resin (A). and an average particle size of 0.5 μm or less as determined by a cumulant method analysis measured by a dynamic light scattering method. 6. The method for producing a pigment-containing resin composition according to claim 5, wherein the drying treatment in step II is freeze-drying. 5. The method for producing an ink for inkjet recording according to claim 4, comprising the following steps I to III.
Step I: A step of mixing and dispersing water, a pigment, a resin (A′), and a neutralizer (b) to obtain an aqueous pigment dispersion (D) Step II: The aqueous pigment dispersion obtained in Step I A step of drying (D) to obtain a pigment-containing resin composition having a volatile substance content of 1% by mass or less Step III: Mixing the pigment-containing resin composition obtained in Step II with a liquid compound , a step of obtaining an inkjet recording ink Here, the water-based pigment dispersion (D) contains the pigment and the resin (A), and the average particle diameter obtained by the cumulant method analysis measured by the dynamic light scattering method is 0.5 μm or less.